If you've never heard of it before, you are probably wondering what it is and why you should care. Code Jam is an annual programming competition sponsored by Google. The top 25 scores receive cash prizes and if you make it to the final round, they fly you to their offices to compete on site. This year, the finals are being held in Dublin!
CodeJam pits developers and programmer against each other to solve complicated software problems in the language of your choice. You can check out the rules page for more information about the competition. You can also use some of the practice tests from years before to give you an idea of what the contest is like.
Be sure to register before May 7th - that's when the first round (qualification) starts!